The present invention relates to a magnetic field sensor, in particular to a magnetic field sensor operating as a zero-crossing switch. Such sensors can be employed as parts of input current converters in electric meters. In such a case a magnetic field generated by the current to be measured is compared to a magnetic reference field, for example a sawtooth reference field, and the zero-crossings of the resultant field are detected by the magnetic field sensor to produce a mark-space modulation. Such sensors can be utilized as position sensors and in connection with micro-switches and for reading magnetic data storage devices.
The deposition of NiFe or NiCo films on semiconductor magnetic field sensors (Magnetic Energy Silicon Micro Transducers) for the purpose of reducing their temperature sensitivity by utilizing the magnetoresistive effect of this type of film is known from the publication:
"Magnetic Energy SMT's", chapter 1, pp. 19-21 and FIG. 14i, S. Middlehoek et al; Modern Electronic Measuring Systems, ed. by P. P. L. Rietgen, Delft University Press, 1978. PA1 "Magnetic Field Micro-Sensor based on Magneto-Resistive Comparators", pp. 176-186, H. P. Baltes et al; Proc. Sensor 1982, ed. by F. Durst et al, Essen, Federal Republic of Germany, 1982. PA1 "Thin Films", chapter 8, pp. 269-339, S. Middlehoek; Magnetic Properties of Materials, ed. by J. Smit, McGraw-Hill, 1971. PA1 a high offset voltage; PA1 slowly rising signals, especially in MOS-technology, and limited opportunity for improvement due to problems of instability; sophisticated circuitry, such as the use of feedback, can result in the reduction of rise-times, but cannot attain the high quality of the magnetic induction/magnetic field-reversal characteristics of a NiFe or a NiCo film. PA1 "Investigation of the Characteristics of Silicon Lateral Magnetotransistors with Two Measuring Collectors", pp. 26-28, I. M. Mitnikova et al; Sov. Phys. Semicond. 12(1), January 1978. PA1 the excellent magnetic induction/magnetic field-reversal hysteresis characteristics of NiFe or NiCo are utilized; PA1 a strong output signal of the order of 10 mV; PA1 the influence of external and internal noise is minimized; PA1 as much as possible of the magnetic field sensor in standard silicon IC technology is realized, and PA1 the complications involved in the technology of extremely thin, current-carrying NiFe or NiCo films are avoided.
Semiconductor magnetic field sensors of the prior art include: magnetoresistors, Hall elements, magnetodiodes, magnistors (also called magnetotransistors), magFET's and Hall-MOSFET's.
The utilization of the magnetoresistive effect of NiFe or NiCo films to perform zero-crossing from the publication:
In comparison to the magnetic induction/magnetic field-reversal hysteresis of NiFe or NiCo films, the magnetoresistive effect of said films is a secondary and therefore less significant effect, displaying a resistivity change of only 1%-2% on switching. Useful signals are obtained with very thin 200 .ANG. films of not too small size with an innate magnetic axis at an angle to the orientation of the imposed magnetic field H.sub.a. The technological problems of such films - fabrication, reliability, etc. are considerable. Furthermore, films employed for this purpose require electrical circuitry with the associated connections. Such films are also loaded by electrical current, and any increase in self-generated noise will impede miniaturisation of the film areas.
By avoiding the use of magnetoresistive zero-crossing detectors, there will result technological simplifications which have a favorable effect on the durability of the films and on power consumption; the films are not loaded with high current densities, they do not require any electrical contacts, they may be made thicker, they produce stronger output signals and the signal shapes are also better defined than when using the magnetoresistive effect.
The inductive operation and inductive detection of NiFe and NiCo films is known from the publication:
In this case, the favorable properties of these films in magnetic induction/magnetic field-reversal hysteresis is utilized. They do, however, require complex hardware and the magnetic field sensor is susceptible to the reception of spurious noise. The requirements of the higher sensitivity and the miniaturisation are conflicting requirements. The output signal of the sensor is only approximately 1 mV.
By avoiding the use of inductive detection of the film signal, the arrangement is simplified and the use of induction coils or induction leads is obviated in contrast to the prior art. The generation of spurious noise typical of induction coils is also eliminated.
Pure semiconductor magnetic field sensors, such as magnetotransistors, have the following disadvantages:
The design and operation of a magnetotransistor are know from the reference: